When running scripts in bash, I have to write ./ in the beginning:
$ ./manage.py syncdb
If I don't, I get an error message:
$ manage.py syncdb
-bash: manage.py: command not found
What is the reason for this? I thought . is an alias for current folder, and therefore these two calls should be equivalent.
I also don't understand why I don't need ./ when running applications, such as:
user:/home/user$ cd /usr/bin
user:/usr/bin$ git
(which runs without ./)
Because on Unix, usually, the current directory is not in $PATH.
When you type a command the shell looks up a list of directories, as specified by the PATH variable. The current directory is not in that list.
The reason for not having the current directory on that list is security.
Let's say you're root and go into another user's directory and type sl instead of ls. If the current directory is in PATH, the shell will try to execute the sl program in that directory (since there is no other sl program). That sl program might be malicious.
It works with ./ because POSIX specifies that a command name that contain a / will be used as a filename directly, suppressing a search in $PATH. You could have used full path for the exact same effect, but ./ is shorter and easier to write.
EDIT
That sl part was just an example. The directories in PATH are searched sequentially and when a match is made that program is executed. So, depending on how PATH looks, typing a normal command may or may not be enough to run the program in the current directory.
When bash interprets the command line, it looks for commands in locations described in the environment variable $PATH. To see it type:
echo $PATH
You will have some paths separated by colons. As you will see the current path . is usually not in $PATH. So Bash cannot find your command if it is in the current directory. You can change it by having:
PATH=$PATH:.
This line adds the current directory in $PATH so you can do:
manage.py syncdb
It is not recommended as it has security issue, plus you can have weird behaviours, as . varies upon the directory you are in :)
Avoid:
PATH=.:$PATH
As you can “mask” some standard command and open the door to security breach :)
Just my two cents.
Your script, when in your home directory will not be found when the shell looks at the $PATH environment variable to find your script.
The ./ says 'look in the current directory for my script rather than looking at all the directories specified in $PATH'.
When you include the '.' you are essentially giving the "full path" to the executable bash script, so your shell does not need to check your PATH variable. Without the '.' your shell will look in your PATH variable (which you can see by running echo $PATH to see if the command you typed lives in any of the folders on your PATH. If it doesn't (as is the case with manage.py) it says it can't find the file. It is considered bad practice to include the current directory on your PATH, which is explained reasonably well here: http://www.faqs.org/faqs/unix-faq/faq/part2/section-13.html
On *nix, unlike Windows, the current directory is usually not in your $PATH variable. So the current directory is not searched when executing commands. You don't need ./ for running applications because these applications are in your $PATH; most likely they are in /bin or /usr/bin.
This question already has some awesome answers, but I wanted to add that, if your executable is on the PATH, and you get very different outputs when you run
./executable
to the ones you get if you run
executable
(let's say you run into error messages with the one and not the other), then the problem could be that you have two different versions of the executable on your machine: one on the path, and the other not.
Check this by running
which executable
and
whereis executable
It fixed my issues...I had three versions of the executable, only one of which was compiled correctly for the environment.
Rationale for the / POSIX PATH rule
The rule was mentioned at: Why do you need ./ (dot-slash) before executable or script name to run it in bash? but I would like to explain why I think that is a good design in more detail.
First, an explicit full version of the rule is:
if the path contains / (e.g. ./someprog, /bin/someprog, ./bin/someprog): CWD is used and PATH isn't
if the path does not contain / (e.g. someprog): PATH is used and CWD isn't
Now, suppose that running:
someprog
would search:
relative to CWD first
relative to PATH after
Then, if you wanted to run /bin/someprog from your distro, and you did:
someprog
it would sometimes work, but others it would fail, because you might be in a directory that contains another unrelated someprog program.
Therefore, you would soon learn that this is not reliable, and you would end up always using absolute paths when you want to use PATH, therefore defeating the purpose of PATH.
This is also why having relative paths in your PATH is a really bad idea. I'm looking at you, node_modules/bin.
Conversely, suppose that running:
./someprog
Would search:
relative to PATH first
relative to CWD after
Then, if you just downloaded a script someprog from a git repository and wanted to run it from CWD, you would never be sure that this is the actual program that would run, because maybe your distro has a:
/bin/someprog
which is in you PATH from some package you installed after drinking too much after Christmas last year.
Therefore, once again, you would be forced to always run local scripts relative to CWD with full paths to know what you are running:
"$(pwd)/someprog"
which would be extremely annoying as well.
Another rule that you might be tempted to come up with would be:
relative paths use only PATH, absolute paths only CWD
but once again this forces users to always use absolute paths for non-PATH scripts with "$(pwd)/someprog".
The / path search rule offers a simple to remember solution to the about problem:
slash: don't use PATH
no slash: only use PATH
which makes it super easy to always know what you are running, by relying on the fact that files in the current directory can be expressed either as ./somefile or somefile, and so it gives special meaning to one of them.
Sometimes, is slightly annoying that you cannot search for some/prog relative to PATH, but I don't see a saner solution to this.
When the script is not in the Path its required to do so. For more info read http://www.tldp.org/LDP/Bash-Beginners-Guide/html/sect_02_01.html
All has great answer on the question, and yes this is only applicable when running it on the current directory not unless you include the absolute path. See my samples below.
Also, the (dot-slash) made sense to me when I've the command on the child folder tmp2 (/tmp/tmp2) and it uses (double dot-slash).
SAMPLE:
[fifiip-172-31-17-12 tmp]$ ./StackO.sh
Hello Stack Overflow
[fifi#ip-172-31-17-12 tmp]$ /tmp/StackO.sh
Hello Stack Overflow
[fifi#ip-172-31-17-12 tmp]$ mkdir tmp2
[fifi#ip-172-31-17-12 tmp]$ cd tmp2/
[fifi#ip-172-31-17-12 tmp2]$ ../StackO.sh
Hello Stack Overflow
https://github.com/ninja-build/ninja/releases
I have downloaded the ninja-win.zip folder and extracted it. When I open it, there is a single .exe file in the entire folder. When I double click it a cmd window flashes for a split second. I have also tried running it as administrator, but the same thing happens. What I don't understand is, what am I expected to do with this .exe file?
You must open a terminal (cmd.exe on Windows) and type something like ninja -f /path/to/buld/file. You may also wish to modify the PATH environment variable so that Windows knows where to find the Ninja executable, depending on your setup.
You can simple download ninja.exe file from this Link
https://github.com/ninja-build/ninja/releases
After that you just have to add the path to your ninja.exe file to your windows environment variables and then you can use ninja commands from anywhere in windows.
1. Open cmd in your Project Directory
2. There are guides on the internet on where to save the Ninja.exe so that it'll be callable in Cmd without specifying directory. Either follow them or:
i, Specify Directory when Calling Ninja. Putting "ninja" in Cmd actually calls Ninja.exe and is the same as something like "C:\users\user1\downloads\Ninja". or:
ii, Save Ninja.exe in the same directory as Project.
3. proceed with rest of the command.
Therefore the Final Command would be:
"C:\users\user\downloads\Ninja.exe" -f "D:\Projects\Project1"
I am new to makefile concept
so to try out if I am able to run and compile c files using word "make"in command prompt I made main.c (which contains main function) ,ttt.c (which contain a function void ttt(int)) , mandar.h (headerfile to include void ttt(int) function in main.c)
when I run this program in cmd using "gcc main.c ttt.c -o main && main",program gets compiled and run properly(so there shouldn't be any error in code)
Now in the same directory I made a file Makefile.txt as follow
image of makefile
Now when I type "make "in cmd following message is shown
image of cmd message
I typed everything exactly the same way as in "head first c " book
did I miss something
this is my first time to ask a question so suggestion regarding improvement of questions are also welcomed
Its not Makefile.txt, you have to name it without any extension just Makefile.
Then run the command.
FIY make by default searches for Makefile in the current working directory. You can change this default behavior by typing make -f filename into the command prompt.
You create your Makefile with some editor (emacs, vim, perhaps notepad). Beware that tab characters are significant in that Makefile and most "action" lines in it should start with a tab, not several spaces.
You then type make in some terminal or command window.
I need to run a program that requires certain inputs that are listed in a input.txt file. I want to be able to call up this file when I execute the program so I can modify the input.txt file if needed before executing the rest of the code.
I'm running on Mac OS X.
What I have is:
call system('notes input.txt')
I get the following message :
sh: notes: command not found
Is there a special way to call the app notes, or is my error somewhere else?
you're not specifying a full filesystem path in the string ("notes input.txt") which the SYSTEM function sends to a command shell. That means you're hoping there's a binary named "notes" somewhere in your shell's $PATH , and your shell is telling you that's not true. The Notes app is not named "notes", and it doesn't live somewhere pointed to by the shell's $PATH. That's why you get this error message. Try passing to the shell the full path of both the binary you want to run, and the file you want to edit:
CALL SYSTEM("/Applications/Notes.app/Contents/MacOS/Notes /path/to/input.txt")
(NB: that path is where the Notes app lives on my Mac; YMMV.)
Try
call system("/Applications/TextEdit.app/Contents/MacOS/TextEdit /path/to/input.text")
The /Applications/TextEdit.app location is a bit misleading as it is actually a folder. In Finder if you option-click on it you can select to view contents (Not sure of the exact wording of the option as I don't have my mac on me at the moment). Alternatively, cd /Applications/TextEdit.app; ls to view the contents. The executable should be stored in a subdirectory as shown above.
i have a program that runs like so:
a.out 23421232
now if i use a.out it will tell me check params and gives an example and closes.
I am curious if there is a way to add command line args when executing my code in vs2008?
Right click the project in Visual Studio. Click Properties. On the Debugging page, there is a Command Arguments property.
Besides using the VS IDE to add parameters for running the program in the IDE, you can also open a command prompt window (Start | Run | cmd) and run the program the same as in Linux, except the .exe extension is optional:
C:\Windows> cd "\Documents and Settings\Administrator\Applications\MyProject"
C:\Documents and Settings\Administrator\Applications\MyProject> myprogram 23421232
VS doesn't normally produce an executable named a.out like most Unix compilers do. Instead, given an input XXX.cpp, it'll produce an executable named XXX.exe.
Adding command line arguments is done by bringing up the project properties (Alt+F7), selecting "Debugging" and then entering the argument(s) in the "Command Arguments" control. There, you'll add JUST the argument "23421232" (or whatever).
Go into the Project Properties window for your executable project.
Under the "Debug" section, you can specify your command line arguments. These will be used when debugging.